1. Field of the Invention
This invention relates to a fastening element, comprising an expandable sleeve to be used with a fastener, such as a screw.
2. Prior art
When mounting objects on walls or the like of hard materials, such as stone, brick, plaster, etc. the traditional way is to drill a comparatively deep hole into the wall, into which a plug of some kind, such as a wooden plug, a plastic plug or a plug of a fibrous material, is inserted. This plug may have a hole, or has a hole made therein, for a suitable screw which forms the actual fastener.
Surveys have shown that in the vast majority of cases the holes in the walls are drilled unnecessarily deep, and unnecessarily long plugs and fasteners are used for the purpose of achieving the intended holding force and resistance to withdrawal. This entails very high, unnecessary costs for labor and materials, and also for tools, since the drill bits are subjected to an unnecessary high wear. Another disadvantage is that the fastening assemblies so far used, comprising a long plug and a long screw or the like, generally undergo such a deformation on mounting that they cannot be removed and used again.
Fastening elements in the form of expandable sleeves have been proposed in the past. Thus, German AS 1 167 509 discloses an expandable sleeve made of a corrugated sheet metal strip. French specification 1 023 043 discloses an expandable sleeve made of a sheet metal strip which has been provided with a plurality of protrusions or embossments by stamping. Neither one of these prior art fastening elements functions satisfactorily. In particular, they do not expand satisfactorily, and they do not engage satisfactorily with the screws and with the internal hole surfaces to provide the required frictional engagement.